Pagurixus aurantiaca, Komai, 2010

Komai, Tomoyuki, 2010, New species and new records of the hermit crab genus Pagurixus Melin, 1939 (Crustacea: Decapoda: Anomura: Paguridae) from the Indo-West Pacific, Journal of Natural History 44 (21 - 22), pp. 1269-1342 : 1279-1285

Pagurixus aurantiaca sp. nov.

( Figures 5–7 )

Material examined

Holotype. Futami Fishing Port , Chichi-jima Island, Ogasawara Islands, 2–3 m, 11 December 2005, trap rope, coll. T. Komai, male SL 1.6 mm ( CBM-ZC 9644 ).

Paratype. Same data as holotype, 1 ovigerous female SL 1.4 mm ( CBM-ZC 9645 ) ; Futami Fishing Port , Chichi-jima Island, 0.5–1.0 m, coral rubble, 10 July 2009, 2 males SL 1.4, 1.6 mm ( CBM-ZC 9647 ) ; Maehama , Chichi-jima Island, 0.5–1.0 m, coral rubble and coral rock, 11 July 2009, 2 males SL 1.5, 1.5 mm, 5 females SL 1.3– 1.5 mm ( CBM-ZC 9648 ) ; Kopepe Beach , Chichi-jima Island, 0.5–1.0 m, coral rock, 13 July 2009, 1 female SL 1.6 mm ( CBM-ZC 9649 ) .

Description

Shield ( Figure 5A ) 1.1–1.2 times as long as broad; anterior margin between rostrum and lateral projections weakly concave; anterolateral margins sloping; dorsal surface slightly convex, with few setae. Rostrum triangular, moderately produced, terminating acutely. Lateral projections obsolete, each with or without marginal or submarginal spinule.

Ocular peduncles ( Figure 5A ) moderately long and stout, about 0.6 length of shield, with few tufts of setae on dorsal surface mesially; cornea slightly dilated, corneal diameter about 0.3 of peduncular length; basal part slightly inflated, slightly wider than cornea. Ocular acicles elongate, subtriangular, without submarginal spinule.

Antennular peduncles ( Figure 5A, B ) moderately stout, overreaching distal corneal margins by about 0.4 length of ultimate segments. Ultimate segment 1.8 times longer than high, with moderately short individual seta on dorsolateral distal portion; ventral surface with only few minute setae. Basal segment with small laterodistal spine on statocyst lobe. Ventral flagellum ( Figure 5B ) with row of sparse setae on lateral and mesial margins.

Antennal peduncles ( Figure 5A ) overreaching distal corneal margins by about 0.1 length of fifth segment. Third segment with small spine at ventromesial distal angle. Second segment with spinule at dorsomesial distal angle; laterodistal projection reaching nearly midlength of fourth segment, terminating in simple spine. First segment with laterodistal spinule; ventromesial distal margin with small projection. Antennal acicle moderately long, arcuate, overreaching base, but not reaching distal corneal margin; mesial and lateral margin with sparse stiff setae. Antennal flagellum relatively short, about 4.0 times longer than shield, each article with two or three short setae distally.

Male right cheliped ( Figure 6A–C ) massive, not particularly elongate. Chela about 1.7 times longer than wide. Dactylus subequal in length to palm, terminating in calcareous claw; dorsomesial margin not delimited; convex dorsal surface with sparse granules, mesial surface with short longitudinal ridges dorsally, ventral surface nearly smooth; dorsomesial margin not delimited; cutting edge with one obtuse calcareous tooth proximally. Palm widened distally, longer than carpus; dorsal surface convex, with sparse granules, particularly numerous laterally and mesially; dorsolateral and dorsomesial margins not delimited; lateral and mesial faces with sparse granules, often forming short, obliquely longitudinal rows; ventral surface smooth. Fixed finger terminating in calcareous claw; cutting edge with one obtuse tooth proximal to midlength. Carpus subequal in length to merus, length subequal to distal width; dorsal surface with few small spinulose tubercles and spiniform setae dorsomesially; lateral surface without trace of division; ventral surface convex, no prominent setae on distal margin. Meral–carpal articulation lacking any pronounced clockwise rotation; dorsal surface of merus smooth; lateral face smooth, ventrolateral margin unarmed; mesial face also smooth, ventromesial margin somewhat produced, slightly dentate; ventral surface smooth, with few short setae. Ischium with smooth ventromesial margin; surfaces smooth.

Female right cheliped ( Figure 7A–C ) distinctly larger than left; surfaces of chela and carpus generally finely granular. Chela 1.6 times longer than broad, subovate with moderately convex lateral margin in dorsal view. Dactylus subequal in length to palm, terminating in small corneous claw; dorsal surface with irregular single row of small tubercles along midline; dorsomesial margin not clearly delimited; mesial surface with longitudinal row of low, distally granular protuberances; ventral surface nearly smooth; cutting edge with row of small corneous teeth on distal half, proximal half faintly dentate. Palm distinctly shorter than carpus; convex dorsal surface with sparse coarse granules, with row of small bifid tubercles in midline and row of small, low protuberances mesially; dorsolateral margin delimited by sharp, granular ridge extending nearly to tip of fixed finger; ventral surface weakly convex, with few short setae. Fixed finger terminating in small corneous claw; cutting edge with row of small calcareous teeth interspersed with minute corneous teeth. Carpus about 1.3 times longer than broad and subequal in length to merus; dorsal surface with coarse granules laterally and row of three spines followed by one tubercle and some spiniform setae mesially, dorsodistal margin unarmed; lateral surface with sparse coarse granules, convex ventrolateral smooth; mesial face smooth, ventromesial margin unarmed; ventral surface strongly convex. Merus smooth on dorsal surface, unarmed on dorsodistal margin; lateral face with sparse coarse granules, ventrolateral margin with one small spine subdistally; mesial face smooth, convex ventromesial margin unarmed, not produced; ventral surface also smooth, only with few short setae. Spines on left cheliped sharper than those in male.

Left cheliped ( Figure 6D–F ) similar between male and female, moderately short, stout. Chela about 2.4 times longer than wide, about 1.2 times longer than carpus. Dactylus longer than palm, terminating in small corneous claw, with sparse tufts of stiff setae on surfaces; dorsal surface smooth; cutting edge with row of small corneous teeth. Palm about half length of carpus; dorsal surface convex, with two longitudinal rows of small spinulose tubercles along midline and several granules mesially; dorsolateral and dorsomesial margins not delimited; lateral surface with scattered short granular rows; mesial and ventral surfaces smooth; scattered tufts of setae on ventral surface (including fixed finger). Fixed finger terminating in small corneous claw, cutting edge with row of small corneous teeth. Carpus somewhat compressed laterally, subequal in length to merus; length 2.5 of distal width and 2.1 of height; dorsolateral margin with row of small spinulose tubercles in distal half, dorsomesial margin with row of four small spines also in distal half; lateral surface nearly perpendicular without trace of division, bearing sparse granules, ventrolateral margin with few spinules at distal angle; mesial surface smooth, with few spiniform setae dorsally; ventral surface convex, with some setae. Merus smooth on dorsal surface, dorsodistal margin unarmed; lateral surface sparsely granular, ventrolateral margin with three small spines distally; mesial face smooth, ventromesial margin without distinct spines; ventral surface weakly convex, smooth, with few setae. Ischium unarmed.

Ambulatory legs ( Figures 5C, F , 7D ) moderately stout, similar on right and left. Dactyli ( Figure 5D, G ) about 1.1 times as long as propodi, 4.9–5.6 times longer than wide, terminating in large corneous claws; dorsal surfaces with sparse short setae; lateral and mesial faces smooth; ventral margins each with seven or eight moderately long corneous spines increasing in size distally. Propodi not tapering distally, 3.6–3.7 times longer than wide in male, about 3.1–3.5 times in female; dorsal surfaces smooth, with sparse setae; lateral faces smooth; ventral margins each with two to six corneous spinules; ventrodistal margins each with paired small corneous spinules. Carpi each with small dorsodistal spine, dorsal surface further each with one spinule proximal to midlength (second) ( Figure 5E ), or unarmed (third). Meri with sparse setae on smooth dorsal and ventral margins; lateral surfaces nearly smooth; ventrolateral distal margins each with one small spine (second) or unarmed (third).

Fourth pereopods ( Figure 5H, I ) subequal and similar in both male and female. Dactyli moderately broad, straight, terminating in small corneous claw, with tuft of short setae distally. Propodi with few setae on dorsal margins; mesial faces nearly flat or slightly convex, with few short setae; propodal rasp of single row of corneous scales. Carpi without prominent tufts of setae on mesial faces.

Coxae of fifth pereopods slightly unequal in male ( Figure 5K ); right coxa with prominent tuft of setae not reaching to left coxa; no development of posteromesial protrusion; papilla-like protrusion of vas deferens apparent. Left coxa with gonopore encircled by tuft of short setae posteriorly; no development of sexual tube or protrusion of vas deference seen. Female with paired gonopores.

Anterior lobe of sixth thoracic sternite ( Figure 5J ) subrectangular, with row of short setae on anterior margin. Eighth thoracic sternite ( Figure 5K ) composed of two slightly unequal, closely set, rounded lobes; ventral surface of each lobe flattened.

Telson ( Figure 5L ) with terminal margins oblique, each bearing 4–6 spinules.

Colouration

In life. Shield translucent, with pale red tinge along anterolateral margins; posterior carapace translucent. Ocular peduncle with two orange-red longitudinal stripes flanking pale brownish median stripe on dorsal surface. Antennular peduncle generally orange-red, flagella whitish. Antennal peduncle generally transparent; fifth segment with orange-red longitudinal stripes laterally and mesially; fourth and second segments each with orange-red spots mesially; flagellum transparent, without conspicuous markings. Right chela white in males, white to orange in females; carpus whitish, with orange-red stripe extending from proximal to midlength along dorsomesial margin and brown obscure longitudinal stripe on midline on dorsal surface; merus generally white, with two obscurely delineated brown stripes either side of dorsal margin (lateral stripe confluent with dorsal stripe on carpus). Left cheliped generally white with orange-red longitudinal stripes; palm with two obscurely delineated stripes on dorsal surface; sloping dorsolateral face of palm orangish, lateral margin whitish, ventrolateral face again orangish, mesial surface whitish; carpus with two dorsal stripes, ventral part of lateral surface orangish; merus with two dorsal stripes flanking white dorsal margin, and with obscure stripe along midline of lateral surface. Ambulatory legs alternated by orange-red and yellowish longitudinal stripes; dactyli with orange-red dorsal and ventral margins, otherwise nearly transparent; propodi each with orange-red stripes on dorsal and ventral margins and on midlines of lateral and mesial surfaces alternated by light yellow; carpi each with orange-red stripes on dorsal margin and on midline of lateral surface alternated by yellow; meri each with orange-red stripes on dorsal and ventral margins and on midline of lateral surface, otherwise transparent or yellowish. Fourth pereopods transparent. Pleon transparent.

Size

Largest male SL 1.6 mm, largest female SL 1.5 mm, ovigerous female SL 1.4 mm.

Distribution

So far known only from Chichi-jima Island, Ogasawara Islands, lower intertidal to 3 m.

Etymology

From the Latin adjective, “ aurantiaca ”, meaning “orange-coloured”, in reference to the orange longitudinal stripes on the chelipeds and ambulatory legs.

Remarks

Pagurixus aurantiaca sp. nov. appears closest to P. nanus Komai and Takada, 2006 and P. dissimilis Osawa and Komai, 2007 . All three species have small spine(s) or spinule(s) in the proximal half of the dorsal surface of the carpus of each second pereopod. From P. nanus , the new species can be distinguished morphologically by the more elongate carpus of the left cheliped and more numerous spines on the ambulatory dactyli (seven or eight versus five). With regard to females, the presence of a row of small protuberances on the mesial face of the dactylus of the right cheliped distinguishes the new species from P. nanus , in which the mesial face of the dactylus is smooth. Pagurixus aurantiaca differs from P. dissimilis in the rounded dorsomesial surface of the dactylus of the right cheliped and the absence of long ventral setae on the merus of the male right cheliped. In P. dissimilis , the dactylus of the right cheliped has a clearly delimited dorsomesial margin; and the merus bears a prominent tuft of long setae on the ventral surface in males. Furthermore, there is no prominent tuft of setae on the dactylus of the left fourth pereopod in P. aurantiaca n. sp., whereas a prominent setal tuft is present on the dactylus of that appendage in P. dissimilis . Colouration in life is quite different between the new species and the two close relatives. Pagurixus aurantiaca has orange-red longitudinal stripes on the ambulatory legs, whereas those appendages of P. nanus and P. dissimilis have dark brown rings on the whitish background.

Figures

Figure 5. Pagurixus aurantiaca sp. nov. holotype, male (shield length 1.61 mm; CBM-ZC 9644). (A) Shield and cephalic appendages, dorsal view; (B) ultimate segment and flagella of left antennule, lateral view; (C) right second pereopod, lateral view; (D) right second pereopod, dactylus, mesial view; (E) right second pereopod, carpus, mesial view; (F) left third pereopod, lateral view; (G) left third pereopod, dactylus, mesial view; (H) left fourth pereopod, lateral view; (I) right fourth pereopod, lateral view; (J) sixth thoracic sternite, ventral view; (K) coxae of fifth pereopods and eighth thoracic sternite, ventral view; (L) telson, dorsal view. Note: Scale bars, 0.5 mm.

Figure 6. Pagurixus aurantiaca sp. nov. holotype, male (shield length 1.61 mm; CBM-ZC 9644). (A) Right chela and carpus, dorsa view; (B) right cheliped, mesial view; (C) right cheliped, lateral view; (D) left chela and carpus, dorsal view; (E) left cheliped, mesial view; (F) left cheliped, lateral view. Note: Scale bar, 0.5 mm.

Figure 7. Pagurixus aurantiaca sp. nov. paratype, female (shield length 1.40 mm; CBM-ZC 9645). (A) Right chela and carpus, dorsal view; (B) right cheliped, mesial view; (C) right cheliped, lateral view; (D) left third pereopod, lateral view. Note: Scale bar, 0.5 mm.